Fish, shellfish and other marine life are kept in bounded natural bodies of water, tanks or aquariums for commercial breeding purposes. The water in such areas is often stagnant having little circulation. In such an environment the oxygen content of the water at various points often becomes too low. This kills marine life there. Thus, the use of mechanical water aerating devices has long been known for keeping the water in such areas properly oxygenated.
Mechanical aerators usually comprise an elongated shaft having a propeller at the end. A motor is provided for turning the shaft. The propeller is arranged to draw water vertically upwardly through a tube or enclosing structure to a point close to or at the surface of the water where the water becomes oxygenated. This oxygenated water then gradually falls back to the bottom of the tank where it is then drawn upwardly again to repeat the cycle. U.S. Pat. Nos. 2,194,037 and 2,515,538 are typical of such aerators.
The aerators described above oxygenate the tank by vertically lifting columns of liquid. The oxygenated water must then fall all the way back to the bottom of the tank for proper oxygentation to occur. This may or may not always occur or the water may have lost much of its oxygen content by the time it reaches the bottom of the tank. Thus, such aerators may not properly oxygenate the lower levels of the tank, especially when they are used in realtively deep tanks. In addition, the horizontal displacement of oxygenated water from such aerators is relatively small. Since such aerators are customarily mounted on the edge of the tank, it is difficult for them to oxygenate the interior portions of the tank. Even when such aerators can traverse the entire area of the tank, they must be moved many times to cover this area.
Another disadvantage with known prior art aerators is that they are relatively complex. For example, the water intake tube to the propeller must be sized sufficiently small so that fish and marine life will not be drawn into the propeller. If that is the case, then the oxygenating capacity of the aerator is relatively small simply because it can displace only small volumes of water. If the intake opening is enlarged, then separate screens are needed to cover the intakes for safety purposes. These screens add to the expense of the aerator. Moreover, a separate structure must be provided to mount the aerating equipment on the tank in which it is being used. This further increases the expense of the aerator.